Isolated converters can be used for providing a galvanic isolation between the input and output of the converter. Such galvanic isolation may be desirable, for example, in photovoltaic (PV) applications where the DC voltage produced by photovoltaic panels is converted to AC voltage and fed to an AC supply network. The use of a non-isolated converter may cause a leakage current due to a stray capacitance of the photovoltaic module that could cause degradation especially in thin film photovoltaic modules. Also, the lack of isolation may compromise the safety of the equipment. In fact, national regulations in some countries specific a galvanic isolation between photovoltaic panels and the AC supply network.
The galvanic isolation may be implemented by using an isolation transformer in connection with the converter. Low frequency transformers can be bulky and heavy. A high frequency transformer can be used to make the system more compact and potentially less expensive. The use of a high frequency transformer in a converter involves the switching frequency of the converter supplying the transformer be high as well. In other words, slow switching speeds involve larger component values, and faster switching speeds enable the use of smaller less-expensive passive components (e.g. transformers, inductors and capacitors) in the converter.
However, while higher switching frequencies would be desirable, characteristics of switch components, such as IGBT (Insulated Gate Bipolar Transistor) and FET (Field Effect Transistor), may set limits to the switching frequencies that can be used. Also the switching losses can increase when the switching frequency is increased. As a result, an increase in the switching frequency of the converter may not be feasible or even possible beyond certain limits.